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(Color online) (a) Optical image of graphene sensor. Graphene films span the ≈6 μm gap between the electrodes within the boxed region (magnified in (g)), (b) schematic cross section of the sensor, (c)-(e) SEM images of the randomly stacked graphene sensors obtained with 3, 5, and 10 ml filtration volumes, respectively. Scale bars are 5 μm, and the red close contour in (d) outlines a typical flake, (f) Raman spectrum of the 3 ml sensor, and (g) magnified optical image taken with the boxed region of (a) with arrow indicating the location where Raman spectrum was collected.
(Color online) (a) Experimental (symbols) and theoretical (lines) conductance (S) vs. filtration volume (ml) for randomly stacked graphene sensors. (b) Resistance of different graphene sensor filtration volumes (normalized to value at room temperature) from 100-300 K, (c) temperature dependent resistance of the 5 ml graphene sensor from 100-400 K. The inset shows the linear fitting of ln(R) to T−1/3 according to the Mott variable range hopping model, indicative of 2-dimensional electron hopping, (d) high resolution transmission electron microscopy (TEM) image of a representative graphene flake, (e) diffraction pattern in inner region of the flake showing the hexagonal structure of crystalline graphene (bright spots), and (f) diffraction pattern near the edge of flake showing characteristic rings due to the loss of long-range order (only weak and diffused diffraction intensity).
(Color online) (a) Sensitivity response (%) of randomly stacked SEG sensors with varying filtration volumes to 100 ms pulse of 1014 toluene molecules. (b) Maximum sensitivity response of SEG sensors vs. graphene filtration volumes from (a). The dashed lines represent maximum responses from polycrystalline (CVD) graphene, polycrystalline (CVD) graphene microribbons, and highly defective CNT sensors to the same dosage of toluene (Ref.17). (c) Sensitivity response of SEG sensors vs. graphene filtration volumes to 100 millisecond pulse of 1014 1,2-dichlorobenzene molecules (Ref. 9). The dashed lines represent maximum responses from polycrystalline (CVD) graphene, polycrystalline (CVD) graphene microribbons, and highly defective CNT sensors to same dosage of 1,2-dichlorobenzene.
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